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Name
Pyometra, Canine
Short Description
Pyometra, cystic endometrial hyperplasia-pyometra complex.
Affected Animals: Pyometra is a common disease in female dogs.
Older, intact female dogs that are one to two months beyond estrus
are at high risk for pyometra. Intact females of all ages that
receive progesterone or estrogen hormones for estrus synchronization
or mismating are also at risk. Spayed animals are rarely affected.
Overview: Pyometra, a serious infection of the uterus, is a
well-recognized disease of female dogs. Pyometra often results from
the animal's own bacteria within the genital tract. Escherichia coli
is the most common bacteria identified in pyometra. Whenever levels
of the reproductive hormone progesterone rise, the uterine lining
becomes susceptible to bacterial infection.
Dogs with pyometra commonly have a vaginal discharge, fever,
lethargy, and a loss of appetite. Affected dogs are often
dehydrated; some may drink and urinate excessively. Some dogs will
appear asymptomatic until after vaginal discharge begins. Others
will go into shock. Laboratory tests often show dehydration-related
abnormalities of electrolyte balance and kidney function. Changes in
the white blood cell count are common. Most patients are diagnosed
using history, clinical signs, physical examination, and abdominal
x-rays.
Pyometra requires prompt treatment. Antibiotics to fight the
infection, and intravenous fluids to correct dehydration-related
abnormalities, are routinely administered. Supportive therapy is
given to correct other organ system dysfunction and to stabilize the
patient. Generally, surgical removal of the uterus and ovaries is
the preferred treatment. However, owners of valuable breeding
animals may elect an intensive medical approach instead of surgery.
Clinical Signs: Signs of pyometra usually appear between one to
two months after the female is in heat, or after the hormone
progesterone has been administered. Common symptoms include vaginal
discharge, anorexia, lethargy, pyrexia, depression, polyuria, and
polydipsia. Some dogs remain asymptomatic except for a thick,
vaginal discharge. This discharge is usually purulent, or pus
containing, but may occasionally be mixed with blood.
Physical examination reveals abdominal distention, an enlarged,
palpable uterus, vaginal discharge if the cervix is open, and
lethargy. A closed-cervix pyometra more likely will result in the
animal showing signs of septicemia, including shock, hypothermia,
dehydration, vomiting, and collapse.
Symptoms: Common symptoms include foul or bloody discharge
from the vulva, loss of appetite, inactivity, fever, depression, and
increased water consumption and urination. The abdomen frequently
enlarges. Severely affected animals may show signs of blood
poisoning, with pale mucous membranes, cold extremities, reduced
body temperature, vomiting or collapse. The presence of vaginal
discharge is variable.
Description: Pyometra refers to uterine infection that occurs
when contaminating bacteria overcome the normal uterine protective
mechanisms. This usually occurs when blood levels of progesterone
are elevated. Progesterone increases may occur naturally, as part of
diestrus or ovarian phase of reproduction, or iatrogenically,
secondary to the administration of reproductive hormones.
As intact female dogs age the uterus may become progressively
thickened and cystic from repeated hormonal stimulation. This
condition called cystic endometrial hyperplasia. Uterine secretions
are greatest during diestrus, the period following estrus, when
blood levels of progesterone hormone are maximal. Some inflammatory
cells are always present in the secretions.
Despite frequent opportunities for bacterial contamination from the
lower reproductive tract, the fluid accumulation in the thickening
uterus remains free of bacterial infection in most dogs. Pyometra
occurs when the excessive uterine secretions become infected with
bacteria.
Escherichia coli is the most common bacteria isolated from the
uterus of patients with pyometra. This bacterium has the ability to
bind specifically to uterine lining cells changed by progesterone.
External sources of estrogen hormone potentiate the effects of
progesterone, increasing the risk for pyometra. Young dogs that are
unlikely to have significant cystic endometrial hyperplasia may
develop uterine infections if hormones are administered. Pyometra
may occur one to eight weeks after an injection of estrogen.
Bacterial infection of the uterus causes increasing inflammation
within the organ and leads to systemic effects. Bacteria or
bacterial toxins may enter the blood stream from the diseased
uterus, leading to the clinical signs described previously. The
severity of the resulting illness is greatly influenced by the
degree of drainage from the uterus. If the cervix is closed, then
fluids and toxins accumulate, like an abscess, with potential for
toxic effects. Rupture or slow leakage from one of the uterine horns
can release inflammatory products into the abdominal cavity, causing
peritonitis. If the cervix is patent, or open, then drainage limits
the accumulation of inflammatory products and bacterial toxins, and
increases the likelihood of early recognition of the problem.
Signs of increased thirst and urination have been linked to the
direct influence of bacterial toxins on the kidneys' urine
concentrating mechanisms. Bacterial infection and toxins may cause
secondary damage to the liver as well. Endotoxic shock alters blood
supply to all tissues and can disrupt normal blood clotting
mechanisms. Microscopic blood clots or clumps of circulating
bacteria can further impact upon the blood supply to vital organs
such as the heart and brain, permitting seizures, cardiac rhythm
disturbances and other grave consequences.
Diagnosis: Diagnosis is based in part on the history,
reproductive status, and clinical signs. Pyometra usually occurs one
to two months after the heat cycle, or estrus. The clinical signs of
vaginal discharge and a palpably enlarged, doughy-feeling uterus are
helpful in establishing the diagnosis, especially if there are
attendant signs of septicemia as well. Laboratory testing and
imaging are frequently used to aid in the diagnosis.
The dog's complete blood count, or CBC, is influenced by the degree
of drainage from the uterus. Patients with a closed cervix and
limited uterine drainage are more likely to show significant
elevations of, or reductions in, the white blood cell count. The
white blood cells are also more likely to appear immature or
unhealthy in those patients. Red blood cell counts are often
reduced; patients with chronic disease frequently have low-grade
anemia. Dehydration can mask this feature by reducing the amount of
water in the bloodstream; consequently, the red blood count appears
higher than it really is.
Blood urea nitrogen, or BUN, and creatinine reflect blood flow to
the kidneys. The level of these nitrogenous waste products in the
blood will frequently rise with dehydration and kidney dysfunction,
which are common in patients with pyometra. Elevated blood protein
levels and disturbed electrolytes will often reflect the state of
dehydration.
The urine may be very dilute, reflecting toxic influences on the
kidneys, or well concentrated as an appropriate response to
dehydration. The urine may contain bacteria or inflammatory cells,
if collected after voiding, due to contamination by the vaginal
discharge. If pyometra is suspected, urine samples are rarely
collected directly from the urinary bladder, via needle aspiration,
because of worries about perforation of the distended, fluid-filled
uterus. Urinary protein levels may be elevated if the kidneys have
been damaged by the presence of chronic infection The vaginal
discharge can be examined microscopically for the presence of white
blood cells and bacteria.
Diagnostic x-rays of the abdominal cavity may demonstrate a
fluid-dense tubular structure. A ground-glass appearance on the
x-ray may suggest fluid accumulation around the diseased uterus if
leakage has contributed to peritonitis. Ultrasound imaging will help
to detect or verify the uterine enlargement, to define uterine size
and wall thickness, and to differentiate between pyometra-related
uterine enlargement and that of pregnancy. Ultrasound imaging is
especially helpful in detecting stump pyometra, which occurs in
spayed females; this condition consists of infected uterine
remnants. Rarely, surgery is required for definitive diagnosis of a
focal or stump pyometra.
Prognosis: Prognosis following ovariohysterectomy, or spay,
is good if there is no uterine rupture or other source of
contamination. Mortality is less than 10 percent. If there is gross
contamination of the abdomen, then open peritoneal drainage is
indicated. These patients will certainly be hospitalized for longer
periods of time, with a need for intensive care. The prognosis for
such patients is guarded.
Dogs with an open cervix that are treated medically with
prostaglandin generally have a good response to treatment, with
complete resolution of infection in 75 to 90 percent of cases. In
contrast, only 25 to 30 percent of dogs with closed cervix pyometra
demonstrate complete resolution of signs. The majority of patients
will require a second series of injections. Unfortunately,
recurrence is common. Perhaps 80 percent of dogs treated medically
will have a recurrence of pyometra. Ovariohysterectomy is then
advised.
Following medical treatment of pyometra, to increase the chances of
conception, the patient should be bred during the next estrus or
heat. Pregnancy may also protect against recurrence of pyometra.
Transmission or Cause: E. coli and other bacteria tend to overgrow in a
hormone-sensitized uterus.
Pyometra may be a natural complication of degenerative and
inflammatory changes that attend cystic endometrial hyperplasia in
the aging intact female. In younger dogs, the problem is most often
linked to progesterone administration for estrus synchronization or
to estrogen given to aid in pregnancy prevention after inadvertent
mating.
Treatment: Pyometra usually necessitates immediate therapy.
Those patients with a closed cervix may be more ill at the time of
diagnosis. Intravenous fluids and antibiotics are routinely
administered to patients that are severely ill, irrespective of the
patency of the cervix. Potent antibiotics are given by injection, in
combinations to target the most common bacterial pathogens.
Supportive measures are customized for individual patient needs,
according to the levels of shock, dehydration, electrolyte
imbalance, organ dysfunction or cardiac arrhythmia. The patient is
stabilized medically, if possible, to prepare for emergency
ovariohysterectomy, or spay, to remove the infected uterus and the
ovaries from the abdominal cavity. Most patients are released two to
three days after uncomplicated surgery. Antibiotics are continued
for seven to 10 days after most procedures.
While surgery is considered the treatment of choice for companion
animals with pyometra, owners of valuable breeding animals may elect
to treat pyometra medically. Stable patients may be given
prostaglandin f2-alpha by injection for several consecutive days to
dilate the cervix, stimulate uterine contractions and to decrease
the blood progesterone level. The dog remains hospitalized for
observation, monitoring for side effects of the prostaglandin or for
worsening condition, and for continued antibiotic administration.
Clinical improvement is expected within the first 48 hours of
medical treatment. Surgery should be considered for patients that
deteriorate. If purulent vaginal discharge persists seven days after
conclusion of treatment, or if other parameters indicate ongoing
infection or uterine enlargement, then repeating the treatment may
be advised, provided that the patient remains physiologically
stable.
Some veterinarians reserve attempted medical evacuation of the
uterus for those patients with an open cervix. Cervical dilation is
inconsistent with prostaglandin f2alpha, thus the drug may cause
expulsion of infected materials into the abdominal cavity through
the fallopian tubes, or direct uterine rupture if administered to
patients with a closed cervix.
Prevention: An elective ovariohysterectomy of the young dog
will virtually eliminate the possibility of pyometra. Avoidance of
estrogen or progesterone administration will decrease the risk of
pyometra in both young and mature pets.
